OBSERVATORY

By HENRY FOUNTAIN

Published: June 8, 2004

A Big Melt

If global warming has the potential for making over the planet, then what happened at the dawn of the Eocene epoch 55 million years ago may best be described as an extreme makeover. That is when a rapid influx of carbon dioxide into the atmosphere caused average temperatures to increase by close to 15 degrees Fahrenheit over 200,000 years.

One theory as to how this occurred involves gas hydrates, reserves of methane frozen in undersea sediments. If these hydrates somehow melted, the theory goes, the methane would bubble into the ocean and atmosphere and quickly be converted to carbon dioxide.

The problem has been figuring out what might have set off such a melting. Now, using seismic imaging, scientists have found evidence of the cause in two basins on the sea floor off Norway.

The evidence is in the form of huge sills, intrusions of molten rock into the basin sediments, and more than 700 pipelike hydrothermal vents or conduits leading up from them. The researchers, who were from Norway, said that the total number of vents in the basins was likely to be three to five times greater than what they found, and that they date from 55 million to 55.8 million years ago, coinciding with the Eocene's start.

The researchers, who reported their findings in the current issue of Nature, suggest that when the hot rock came in contact with the sediments, the methane in them bubbled out, forming the hydrothermal vents. Further research is needed, the scientists say, but the volume of the sills and the large number of vents make it likely that the intrusion of the molten rock could have set off the extreme warming.

Protecting a Turtle Species

The leatherback turtle is one of the most endangered marine species, with the subspecies found in the Pacific near extinction and its Atlantic cousin not faring much better. The turtles suffer at their nesting beaches, where light pollution and other problems reduce the survivability of young, and in the open ocean, where they become entangled in the gear of long-line fishing boats and drown.

Conservationists have hoped that by better understanding the migratory patterns of leatherbacks they could come up with fishing restrictions that might increase the turtles' survival chances. Now, two research teams, one French and one British, have used satellite tracking to monitor the movement of leatherbacks in the Atlantic.

Their results, also in the current issue of Nature, show that turtles from beaches in French Guiana and Suriname, the only major Atlantic nesting sites that remain, follow two basic patterns. Some head north, crossing the Gulf Stream into the North Atlantic, while others head due east toward Africa.

The turtles in the British study carried devices that measured their foraging dives. The study showed they spent more than half their time below about 30 feet and rarely dived below about 800. Unfortunately for the turtles, that range coincides with that used by most long-line fishing boats for their multihooked lines.

Because of this, and because the area traveled by the turtles coincides with so much fishing territory, both research groups say new approaches need to be adopted and enforced throughout the Atlantic to protect the few turtles left.

Caution: Whale Crossing

An example of a new conservation approach can be found in proposed rules for ships intended to protect North Atlantic right whales. The rules, developed by the National Marine Fisheries Service, call for speed restrictions and route changes for ships within 30 miles of ports and other parts of the Eastern Seaboard.

North Atlantic right whales are highly endangered, and collisions with ships are a major reason for that. From 1991 to 2002, ships killed 14 whales. The speed restrictions, down to 10 to 14 knots, are to give whales a chance to get out of the way of oncoming ships.

Tasty, and a Great Source of DNA

When direct study is out of the question, scientists often have to use proxies. For instance, researchers cannot actually experience what the climate was like thousands of years ago, so they examine things like sediment from lakes or ice cores from glaciers for clues.

But the proxy that Lisa Matisoo-Smith of the University of Auckland used to study the origins of Polynesians was a little unusual. Unable to research genetic variations in ancient people, she turned to the next best thing -- rats.

Dr. Matisoo-Smith and a colleague, J.H. Robins, examined the variations in mitochondrial DNA of ancient and modern samples of a rat species, Rattus exulans, from Bougainville, New Britain and other Polynesian islands. This species was taken along by the Lapita people in their outrigger canoes when they settled parts of Oceania roughly 3,000 years ago.

The analysis, reported in The Proceedings of the National Academy of Sciences, shows three distinct groups of rats. Similarities between rats in certain locations suggests that rather than a rapid migration from Taiwan into Oceania, as some anthropologists have proposed, the Lapita influx was probably gradual, with much mixing of cultures along the way. ''It was not a hermetically sealed culture moving through the Pacific,'' Dr. Matisoo-Smith said. ''There was a lot of interaction going on.''

There is much evidence that the Lapita people took R. exulans along for food. Unlike European rats, Dr. Matisoo-Smith said, exulans do not swim and dislike wet conditions. So it is unlikely that they accidentally reached the islands through infested ships.

As a food source, the rats do not require much effort. The Lapita would have just had to release them on the islands they settled, and rats being rats, there would soon be plenty for eating.

That also left plenty of rat remains for analysis. Ancient human remains in the Pacific are rare and off-limits for study, Dr. Matisoo-Smith said. So there was no hope of comparing genetic variations in old and new human tissue. ''But,'' she said, ''there are lots and lots of rat bones around.''